1. Field of the Invention
This invention relates to a pyroelectric infrared detector. This invention also relates to a method of fabricating a pyroelectric infrared detector.
2. Description of the Prior Art
R. Takayama et al reported high sensitive pyroelectric linear array infrared sensors fabricated by using highly c-axis-oriented and spontaneous polarized La-modified PbTiO.sub.3 (PLT) thin films (Journal of Applied Physics 63(12), 15 Jun. 1988, p5868-5872). The PLT thin films were deposited on (100)-orientated Pt thin film on (100)-cleaved MgO single crystals by RF magnetron sputtering. The PLT thin films had high figures of merit for voltage responsivity (Rv) and specific detectivity (D*) without a poling treatment.
Since the pyroelectric infrared sensor reported by R. Takayama et al uses an MgO single crystal as a substrate, it is generally difficult to form the pyroelectric film and an external circuit on a common substrate. The MgO substrate has a high thermal conductivity. Thus, a portion of the MgO substrate which extends directly below a major part of the pyroelectric film is etched off to suppress heat transfer from the pyroelectric film to the substrate to attain a high infrared sensitivity.
Japanese published unexamined patent application 4-170077 discloses a pyroelectric infrared detector fabricated as follows. A pyroelectric film was formed on a first substrate made of an MgO single crystal. The pyroelectric film and exposed portions of the first substrate were coated with an organic film. A second substrate having a central opening was bonded to the organic film by adhesive. Finally, the first substrate was etched off to complete the pyroelectric infrared detector in which the pyroelectric film was supported on the second substrate via the organic film. The pyroelectric film was located above the opening in the second substrate.
In the pyroelectric infrared detector of Japanese application 4-170077, the pyroelectric film was made of Pb.sub.x La.sub.y Ti.sub.z Zr.sub.w O.sub.3 where the atomic fractions "x", "y", "z", and "w" satisfied one of the following three different conditions (a), (b), and (c):
(a) 0.7.ltoreq.x.ltoreq.1, 0.9.ltoreq.x+y&lt;1, 0.95.ltoreq.z.ltoreq.1, w=0 PA1 (b) x=1, y=0, 0.45.ltoreq.z&lt;1, z+w=1 PA1 (c) 0.83.ltoreq.x.ltoreq.1, x+y=1, 0.5.ltoreq.z&lt;1, 0.96.ltoreq.z+w.ltoreq.1
During the fabrication of the pyroelectric infrared detector of Japanese application 4-170077, the first substrate made of MgO was etched off as previously described. Generally, the removal of the MgO substrate is disadvantageous in cost and time. The opening extends through walls of the second substrate. Thus, during the etching process, etchant tended to reach the organic film and the pyroelectric film via the opening in the second substrate. In this case, the etchant adversely affected the organic film and the pyroelectric film. In some cases, the pyroelectric film was broken. Thus, it is difficult to improve the yield of detectors.